Advances in optical electronics have led the way to more powerful computers, faster and clearer communications and high resolution image displays, among other developments. Progress in the development of optical electronics has been based almost exclusively on III-V semiconductors, e.g., gallium arsenide, or II-VI compounds. These compound semiconductors have direct band gaps which permit rapid recombination of carriers, thus releasing the full band gap energy as light. Most semiconductor diode lasers and LEDs are based on III-V compounds.
Silicon, on the other hand, is the preferred material for microelectronic devices other than optical electronics. Silicon crystals are much easier and cheaper to make, and processing of the devices is considerably less complicated than that of compound semiconductor devices. Silicon's band gap is indirect, resulting in slow recombination rates. Further, its band gap (1.09 eV) is too narrow to generate visible light. Thus, optical electronics systems have primarily been made of hybrid components of gallium arsenide and silicon, in spite of efforts to combine the two substances on a single chip.
Recently it has been determined that by etching nanometer structures in silicon wafers, the silicon can be transformed into a direct band gap material. These structures have been labeled "silicon quantum wires" and are thin columns in which electrons take on higher energy states than they can in larger silicon structures. This behavior has been explained as a quantum confinement due to the very small dimensions of the silicon wire which leads to an increase in effective band gap energy.
Porous silicon is made by electrochemically etching single-crystal silicon in solutions containing hydrofluoric acid (HF). Since a primary interest in photoluminescence of silicon is to convert electrical to optical signals directly and efficiently on a silicon chip, it is necessary to devise a means for incorporating the porous silicon structure into a circuit directly on the single-crystal substrate. It is to such a means that the present invention is directed.